1. Field of the Invention
The invention relates to a semiconductor light-emitting device comprising of a group III-V nitride base semiconductor (hereafter referred to as a nitride base semiconductor) such as BN(boron nitride), GaN(gallium nitride), AlN(aluminum nitride), InN(indium nitride), TlN(thallium nitride), or crystal mixtures of these nitrides, and capable of emitting white light, and a method of fabricating the semiconductor light-emitting device.
2. Description of Prior Art
White light-emitting devices using light-emitting diodes are under development in order to invent a white light source having a low power consumption, high reliability and a long-life.
For example, a light-emitting device in which three light-emitting diodes emitting light beams of primary colors, red, green and blue respectively are arranged on one stem has been known. Such a light-emitting device is capable of emitting white light by blending red light, green light and blue light emitted from each light-emitting diode.
JP 232627/1997 A discloses a light-emitting diode in which three emission layers emitting red light, green light and blue light respectively are formed on one substrate. Such a light-emitting diode can emit white light by blending light beams of three colors emitted from each emission layer.
Also JP 97200/1998 A discloses a method for obtaining white light by incorporating a fluorescent material into a light-emitting diode emitting blue light. In this case, for example, the fluorescent material such as YAG based materials is coated over a surface of a GaN base light-emitting diode emitting blue light in a resin molding process.
The other method also has been known that ZnSe base light-emitting diode can obtain white light by blending blue light emitted from an emission layer composed of ZnSe base material and yellow fluorescence emitted from ZnSe substrate.
The above mentioned light-emitting device comprising three light-emitting diodes emitting light of three different colors respectively requires a plurality of light-emitting diodes to obtain white light. Thus the fabricating process of the device is complicated, resulting in time-consuming and costly manufacturing process.
As to the light-emitting diode having three emission layers in JP 232627/1997 A, the fabricating process of three emission layers is complicated, resulting in time-consuming and costly manufacturing process. In addition, the emission layer composed of InGaN needs to contain a large proportion of In composition in order to emit red light, but such an emission layer is difficult to grow.
As to the method of obtaining white light by incorporating the fluorescent material into the light-emitting diode, disclosed in JP 97200/1998 A, the method needs not only a growing process of semiconductor layers but also a coating process of the fluorescent material. Such a light-emitting diode requires complicated fabricating processes, resulting in time-consuming and costly manufacturing process.
As to the ZnSe base white light-emitting diode fabricated by combining the ZnSe base emission layer emitting blue light and the ZnSe substrate emitting yellow fluorescence, the ZnSe material suffers serious deterioration caused by continued energization, therefore, such a light-emitting diode has a short-life and a low reliability.
It is an object of the invention to provide a semiconductor light-emitting device which is capable of extracting white light, manufactured readily and highly reliable, and a method of fabricating the device.
A semiconductor light-emitting device according to the invention comprises an emission layer composed of a group III nitride base semiconductor and generating light by carrier injection, and a fluorescent layer composed of the group III nitride base semiconductor and generating light by excitation from the light generated in the emission layer. The light generated in the emission layer is different in a peak wavelength from the light generated in the fluorescent layer.
The semiconductor light-emitting device of the present invention can readily emit white light by blending the light from the emission layer and the light from the fluorescent layer and extracting the blended light, due to the difference in the peak wavelength of both lights.
In manufacturing the semiconductor light-emitting device, the emission layer and the fluorescent layer can be grown in sequence in a same way. Therefore, manufacturing the semiconductor light-emitting device is readily, resulting in high yield and a low cost.
Also the semiconductor light-emitting device comprises the emission layer and the fluorescent layer composed of the group III nitride base semiconductors, which are chemically stable materials. Because of this, the emission layer and the fluorescent layer can be energized without deterioration. Therefore, the semiconductor light-emitting device with a long life and a high reliability can be realized.
It is preferable that the light from the emission layer and the light from the fluorescent layer make a color complement to each other. In this case, white light emission can be obtained by mixing the light from the light-emission layer and the light from the fluorescent layer and extracting the mixed light.
It is also preferable that the emission layer and the fluorescent layer are arranged so that the light generated in the emission layer passes through the fluorescent layer. Consequently, the light generated in the emission layer is mixed with the light generated in the fluorescent layer, obtaining white light.
The emission layer may be formed on the fluorescent layer so that the light from the emission layer and the light from the fluorescent layer are extracted from the fluorescent layer""s side. Conversely, the fluorescent layer may be formed on the emission layer so that the light from the emission layer and the light from the fluorescent layer are extracted from the fluorescent layer""s side.
As to the semiconductor light-emitting device including the fluorescent layer on the emission layer, at first, the emission layer having good crystallinity is formed, and next, the fluorescent layer is formed thereon. In such a semiconductor light-emitting device, the emission layer is not affected by crystallinity of the fluorescent layer, maintaining good crystalline state. Therefore, properties of the semiconductor light-emitting device can be improved.
The group III nitride base semiconductor may include at least one of aluminum, gallium, and indium. The emission layer containing the group III nitride base semiconductor may have an arbitrary emission wavelength in a range between 380-650 nm by controlling the composition in the group III nitride base semiconductor. Then, the composition is so controlled that the fluorescent layer emits light having a wavelength complemented in color for light generated in the emission layer.
The fluorescent layer may be composed of a silicon-doped gallium nitride. The silicon-doped nitride gallium of the fluorescent layer is doped with a higher concentration of silicon than a silicon-doped gallium nitride having sufficient good crystallinity, so the fluorescent layer including such a silicon-doped gallium nitride has good fluorescent properties. When the fluorescent layer is excited by light generated in the emission layer, the fluorescent layer generates intensive yellow light with a wavelength in a range between approximately 550-650 nm. Because the yellow light is the complement in color for light generated in the emission layer, white light can be obtained by mixing both lights and extracting the mixed light.
A fluorescent layer may be composed of a carbon-doped gallium nitride. The fluorescent layer including nitride gallium doped with carbon has good fluorescent properties. When the fluorescent layer is excited by light generated in the emission layer, the fluorescent layer generates intensive yellow light with a wavelength in a range between approximately 550-650 nm. Because the yellow light is the complement in color for light generated in the emission layer, white light can be obtained by mixing both lights and extracting the mixed light.
A fluorescent layer may be composed of an undoped gallium nitride. In the growth process, the fluorescent layer is supplied with source gas in which proportion of Nitrogen element and Gallium element to the source gas is set lower than that of the source gas supplied to a fluorescent layer with sufficient good crystallinity, therefore the fluorescent layer has good fluorescent properties. When the fluorescent layer is excited by the light generated in the emission layer, the fluorescent layer generates intensive yellow light with a wavelength in a range between approximately 550-650 nm. Because the yellow light is the complement in color for light generated in the emission layer, white light can be obtained by mixing both lights and extracting the mixed light.
A method of fabricating a semiconductor light-emitting device according to the present invention includes a process of forming an emission layer composed of a group III nitride base semiconductor and emitting light by carrier injection and a process of forming a fluorescent layer composed of a group III nitride base semiconductor, being excited by light from the emission layer and emitting light having a peak wavelength different from that of light generated in the emission layer.
The semiconductor light-emitting device fabricated through the method of the invention can readily obtain white light emission, due to the difference in the peak wavelength between light from the emission layer and light from the fluorescent layer, by mixing both lights and extracting the mixed light.
According to the fabricating method of the semiconductor light-emitting device, the emission layer and the fluorescent layer can be grown in sequence in the same way. Therefore, manufacturing the semiconductor light-emitting device is easy, resulting in high yield and a low cost.
Also the semiconductor light-emitting device fabricated through the above described method comprises the emission layer and the fluorescent layer composed of the group III nitride base semiconductors, which are chemically stable materials. Because of this, the emission layer and the fluorescent layer can be energized without deterioration. Therefore, the method in the invention can realize the semiconductor light-emitting device with a long life and high reliability.
It is preferable that light from the emission layer and light from the fluorescent layer make a color complement to each other. Consequently, white light emission can be obtained by mixing the light from the light-emission layer and the light from the fluorescent layer and extracting the mixed light.
Processes of forming the fluorescent layer may include a process of doping silicon to the group III nitride base semiconductor. A concentration of silicon to be doped may be so set that the III nitride base semiconductor exhibits fluorescent properties. Further processes of forming the fluorescent layer may include a process of doping carbon to the III nitride base semiconductor. Furthermore, processes of forming the fluorescent layer may include a process of supplying source gas including Nitrogen element and group III elements. The proportion of Nitrogen element and the group III elements in source gas may be so set that the group III nitride base semiconductor exhibits fluorescent properties.
According to the above mentioned methods, it is possible to form the fluorescent layer with good fluorescent properties.
The group III nitride base semiconductor may include at least one of aluminum, gallium, and indium. An emission layer composed of such a group III nitride base semiconductor can be set to emit an arbitrary emission wavelength in a range between 380-650 nm by controlling the proportion of the compositions in the group III nitride base semiconductor. The compositions are so controlled that the fluorescent layer emits light which is the complement for light emitted from the emission layer.